1. FIELD OF THE INVENTION
The present invention relates to a material for gas separation. More particularly, it relates to a material for gas separation composed of a reaction mixture obtained by mixing a copper compound and a benzoin and/or an ascorbic acid in a solvent, particularly at least one member selected from the group consisting of an imidazole, a pyridine and a polyethylenepolyamine, and to a composition for gas separation comprising such a reaction mixture or a reaction product of oxygen with such a reaction mixture and an alkene complex of palladium. The present invention relates also to a selective gas permeation membrane having the material or composition for gas separation supported on a supporting membrane and to a method for gas separation wherein such a selective gas permeation membrane is used. Further, the present invention relates to a method for gas separation wherein the material or composition for gas separation is used as a selective gas absorbing solution.
2. DISCUSSION OF BACKGROUND
Separation technique useful for the separation, concentration and purification of carbon monoxide from a gas formed by the steam refining or partial oxidation of hydrocarbons such as natural gas, light naphtha or heavy oil or from an iron making byproduct gas such as converter gas, blast furnace gas or coke oven gas, is important in the chemical industry for the purification of the starting material gas in the ammonia synthesis and for the production of starting materials for the preparation of various chemical industrial products.
For the separation and concentration of carbon monoxide from a gas mixture containing carbon monoxide, various methods have been practically employed such as a cryogenic separation method, an absorbing solution method, an adsorption method and a membrane method. However, each of these methods has its own technical problems.
The cryogenic separation method requires a complicated freezing and heat recovery system, and the operational temperature is low, whereby it is necessary to use a high quality material as the material of the apparatus, thus leading to a high installation cost. Further, for the low temperature operation, the power consumption is large. Further, in order to prevent clogging in the apparatus, it is necessary to install a pretreatment installation and preliminarily completely remove impurities from the gas.
For the absorbing solution method, it has been in practice since long ago to use an aqueous cuprous chloride solution acidified with hydrochloric acid or an ammoniacal aqueous cuprous chloride solution as the absorbing solution for carbon monoxide. However, this method has difficulties such as the highly corrosive property of the absorbing solution, the formation of precipitates and the high installation cost. In recent years, an absorbing solution method which is called COSORB process wherein a toluene solution of a copper aluminum chloride is used as the absorbing solution for carbon monoxide, has been developed and practically in use. According to this method, the impurities in the gas, particularly carbon dioxide which must have been removed by pretreatment in the above-mentioned method, are not absorbed, whereby the separated and purified carbon monoxide has a high purity. On the other hand, when contacted with a gas mixture containing water, hydrogen sulfide or ammonia, the copper chloride-aluminum chloride complex in the absorbing solution irreversibly reacts with these impurities, whereby the absorbing power of the absorbing solution for carbon monoxide will be impaired. Further, heating is required for releasing carbon monoxide from the absorbing solution.
With respect to the adsorbing method, an adsorbing method employing zeolite as the adsorber has recently been developed, and operation of a practical machine has started for e.g. converter gas. According to this method, the operation can be conducted at room temperature, and the apparatus may be of a small scale. Further, as opposed to the conventional absorbing solution method, this method is free from a problem of the evaporation of the solvent, and a stabilized catalytic operation can be ensured. On the other hand, the difference in the adsorbing properties among gases of different types is small, and it is rather difficult to obtain highly pure carbon monoxide by a single step particularly when the carbon monoxide concentration is low, although the method may be suitable for use when the concentration of carbon monoxide in the gas is high as in the case of converter gas. Further, in the case of zeolite, carbon dioxide is more readily adsorbed than carbon monoxide, and therefore, it is necessary to preliminarily remove carbon dioxide. Furthermore, the adsorption is required to be conducted under pressure, and the desorption is required to be conducted under reduced pressure. Thus, the operational cost is large.
Finally, with respect to the membrane method, various polymer membranes have been studied for membranes for the separation of gas mixtures. However, when a usual polymer membrane is used alone, carbon monoxide is less permeable than other gas such as hydrogen. Accordingly, this method may be practically useful for the purpose of separating hydrogen from a gas mixture containing an excess amount of hydrogen by letting it pass through the membrane to change the proportions of hydrogen and carbon monoxide in the remaining gas. However, it is not practically useful for the purpose of obtaining carbon monoxide at a high concentration because the selectivity is low. With a polymer membrane, the gas permeability constant is small. However, if the film is liquid, the gas solubility constant or diffusion constant is large, and it is thereby possible to have a large permeability constant. Further, when a substance having an reversible interaction selectively with a certain gas, is contained in such a liquid film, the permeability of the gas can further be increased. On the other hand, the selectivity of a film may be provided also by the difference in the solubility in the film of various gases or by the diffusion rate in the film of various gases. Therefore, when a substance having a reversible interaction selectively with a certain gas, is contained in the film, as mentioned above, the solubility of the particular gas can be increased exclusively, whereby the selectivity can be made remarkably high. Many instances have been known with respect to such films containing substances having an reversible interaction selectively with certain gases. For example, there have been known the separation of carbon dioxide by means of an aqueous solution of an alkali metal hydrogencarbonate (Japanese Examined Patent Publication No. 1176/1970), the separation of an olefin by means of an aqueous silver nitrate solution (Japanese Examined Patent Publication No. 31842/1978) and the separation of nitrogen monoxide by means of a formamide solution of ferrous chloride (A.I.Ch.E. Journal, vol. 16, No. 3, p. 405, 1970). These liquid films are used as supported on membranes as supporting members. Further, for the separation of carbon monoxide, an aqueous hydrochloric acid solution of copper chloride is known. This method has a drawback that it is necessary to use a highly concentrated aqueous hydrochloric acid solution. Further, when the secondary side (effluent side) of the permeation is kept under reduced pressure, there is a drawback that hydrochloride gas tends to permeate and mingle with other gas.
As described in the foregoing, various methods for separating carbon monoxide have been developed, but each of them has its own merits and demerits, and a further improvement has been desired with respect to the drawbacks.